The invention relates to apparatus for sensing and transmitting environmental information.
As will become apparent, the present invention, which will be referred to as an electric field meter, has been developed primarily for the purpose of measuring the growth of electrical fields in thunderclouds. For this reason, the ensuing discussion will be particularly with regard to the thundercloud application. Other uses, however, are considered to be within the present inventive scope.
There have been a number of previous efforts directed at obtaining reliable data regarding the growth and behavior of electric fields in thunderclouds. In particular, various investigators and authors have predicted that the behavior of the electric field in a cloud should be different than that at ground. For one reason, the electric field at the ground is affected by point discharge from the ground. Also, it is a fact that the air outside of clouds, especially at high altitudes, has known finite conductivity. Consequently, estimates based upon measurements made outside of a cloud, such as at ground level, are not reliable and their unreliability leaves unresolved several important questions. For example, it is important to determine how the behavior of the electric field in the cloud compares with that at the ground. Also, reliable data is needed regarding the total quantity of the charge in regions affected by lightning as well as such matters as the behavior of the electric field as a function of time inside a cloud at a point fixed relative to the cloud. Obviously, data capable of providing reliable estimates must be obtained from positions directly within the cloud. Also, it is important, particularly in obtaining the so-called `recovery curves` (electrical field strength vs. time between lightning flashes) to assure to the maximum possible extent that the measurements are obtained from a fixed disposition relative to the cloud. To obtain such data, some previous investigators have utilized slowly moving vehicles, such as balloons or parachutes to carry the sensing instrumentation into cloud formations. For example, the following authors have described results obtained by releasing free balloons with instruments that measured the corona current through a long vertical wire:
Simpson, G. C. and Scrase, F. J., 1937, `The distribution of electricity in thunderclouds,` Proc. R. Soc. London A, 161, pp. 308-352. PA1 Simpson, G. C. and Robinson, G. D., 1940, `The distribution of electricity in thunderclouds, II,` Proc. R. Soc. London A, 177, pp. 281-329 PA1 Chapman, S, 1953, `Thundercloud electrification in relation to rain and snow particles,` Thunderstorm Electricity, Chicago Press, pp. 207-230 PA1 Yuan, C., Chiang, P., Jan, L., Chou, S., and Chen, T., 1965, `A stong electrical field radiosonde and analysis of results obtained in thunderclouds,`Ch'i-hsiang Hsueh-pao (Acta Meteorologica Sinica), 35, pp. 440-448.
However, although these authors were able to deduce the sign of the vertical component of the field, their estimates of the magnitude of vertical component were very rough because magnitude is related to the corona current by a non-linear function that varies with altitude. Other recorded data has been obtained by W. H. Evans, 1969, `Electric fields and conductivity in thunderclouds,` J. Geophys. Res., 74, pp. 939-948, and W. D. Rust and C. B. Moore, 1974, `Electrical conditions near the bases of thunderclouds over New Mexico,`Quart. J. R. Met. Soc., 100, pp. 450-468. The data reported by Evans was obtained by employing parachuteborne instruments while the Rust and Moore records were obtained with the use of a captive balloon. J. A. Chalmers in a review appearing in 1967, Atmospheric Electricity, Pergamon Press, also describes a so-called "electronic flux meter" which has proven to be a useful device that in some respects is related to the present meter.
The present invention is particularly concerned with providing an improved electric field meter which is slowly moved vertically up and down through a cloud formation preferably by a balloon and a parachute. In particular, it provides a combination field sensor and telemetry antenna by means of which the sensed information can be transmitted to a data-collection center for comparison with other data obtained at ground level.
The objects of the invention are concerned generally with obtaining reliable data relative to the matters which have been discussed. Also, as will become apparent, the invention seeks to obtain this data by the use of expendable apparatus or, in other words, apparatus that is so simple and inexpensive that its recovery costs normally would exceed its fabrication cost.